FIELD OF THE INVENTION
The invention lies in the electrical and electronic arts. More specifically, the invention relates to a circuit configuration for providing a substantially load-independent output voltage, having the following features:
a current control assembly for controlling the mains current consumption, having an AC voltage terminal for applying a mains voltage and having two output terminals; PA1 a rectifier assembly which is connected to the output terminals of the current control assembly and has output terminals to which the output voltage is applied; PA1 a voltage measurement arrangement, for providing a voltage signal at an output terminal, which is connected to the output terminals of the rectifier assembly; PA1 a feedback branch having a voltage control arrangement for feeding the voltage signal back to the current control assembly. PA1 a current control assembly for controlling a mains current consumption, the current control assembly having an AC voltage terminal for receiving a mains voltage and having two output terminals; PA1 a rectifier assembly connected to the output terminals of the current control assembly, the rectifier assembly having output terminals carrying an output voltage; PA1 a voltage measurement arrangement connected to the output terminals of the rectifier assembly, the voltage measurement arrangement having an output terminal outputting a voltage signal; and PA1 a feedback branch having a voltage control arrangement connected between the output terminal of the voltage measurement arrangement and the current control assembly for feeding the voltage signal to the current control assembly, the voltage control arrangement including a sample and hold circuit for evaluating the voltage signal during predeterminable sampling intervals.
Such circuit configurations, also referred to as "power factor controllers," are used for example in switched mode power supplies. As the load, a chopper-type regulator, for supplying a consumer with a DC voltage, is in this case connected to the output terminals of the rectifier assembly. The object of the circuit configuration according to the generic type is thereby to make the output voltage available as a DC voltage at least approximately load-independently and with as sinusoidal a mains current consumption as possible. The requirement for sinusoidal mains current consumption by such switched mode power supplies is regulated in Europe, for example, by an EC regulation that power supplies, for example for computers, with a power consumption of more than 75 W must guarantee a mains current consumption with a sinusoidal shape corresponding to the mains voltage.
The task of the current control assembly is, on the one hand, to create sinusoidal mains current consumption through its input terminals and, on the other hand, to control the power delivered at its output terminals to the rectifier assembly in such a way that as constant a DC voltage as possible is applied as the output voltage to the output terminals of the rectifier assembly, this voltage remaining as stable as possible even when the load fluctuates. The voltage measurement arrangement connected between the output terminals of the rectifier assembly produces, from this DC voltage, a voltage signal which is dependent on the latter and is fed back to the current control assembly via the feedback branch. A control signal, fed back to the current control assembly and applied to the output of the feedback branch, is used to adjust the mains current consumption, or power consumption, when there are fluctuations in the DC voltage due to the load, until the predetermined value of the output voltage is obtained.
The output voltage applied to the output terminals of the rectifier assembly is not an ideal DC voltage, but has residual ripple whose frequency depends on the frequency of the mains voltage.
In order to prevent the ripple of the output voltage, or of the voltage signal, from being fed back to the current control assembly, in known circuit configurations of the generic type the voltage control arrangement present in the feedback branch has an integrator with a time constant which is large compared with the period of the mains voltage.
Integrating the voltage signal, or a signal representing the difference between the voltage signal and a reference signal, over a comparatively long time window does, however, have the disadvantage that, owing to the time constant of the integrator, sudden load changes and sudden changes in the output voltage which result from this are only detected with a time lag by the current control assembly. Especially at times when there is no load at all, there is a risk that the circuit configuration will be destroyed during this time lag by the inevitable rise in the output voltage, unless extra circuitry for limiting the output voltage is employed.